The desire for portable multiband radio operation has grown significantly over recent years. The ability to communicate over different frequency bands, using different protocols and operating modes allows a wider variety of options for users. For example the ability to transmit, receive and process voice, data, and video using one device as opposed to carrying several different devices is highly advantageous in the public safety arena. Public safety personnel often work in environments where access to a variety of communication mediums is highly relevant such as law enforcement, fire departments, and search and rescue.
Two types of radio operation that are deemed desirable to have available in one overall system for public safety applications are: Long-Term Evolution (LTE) operation for high speed, full-duplex data and Land Mobile Radio (LMR) operation for half-duplex voice operation.
LTE full-duplex operation which facilitates high-speed data communications takes place in 3GPP standardized bands. LTE band 13 uplink frequencies cover 777-787 MHz and downlink frequencies cover 746-756 MHz. LTE band 14 uplink frequencies cover 788-798 MHz and downlink frequencies cover 758-768 MHz. LTE band 14 has been designated for public safety operations in the US.
LMR radio operates as a half-duplex, voice radio in UHF frequency bands. For public safety narrowband applications the UHF frequency bands of operation have been designated 799 to 805 and 805 to 817 megahertz (MHz)/769 to 775 and 851 to 862 MHz—also referred to as the 700/800 MHz band. Thus, the spectral allocations of the LTE band and the LMR public safety narrowband are close.
From an implementation standpoint, in order for a portable radio to include both LTE and LMR transceivers in the same handheld unit, both transceivers may be physically close to one another. The spectrum allocations of the LTE band being spectrally near the LMR narrowband voice band and the physical proximity LTE transceiver and LMR transceiver within the handheld unit can cause problems when certain transmit and receive conditions are all active simultaneously—which is feasible in multiband radios.
Some energy from an LMR transmit signal may combine with energy from an LTE transmit signal after the LTE antenna, while the LTE receiver is active thereby creating spurious emissions. For example, B14 receive problems can occur when the LMR TX is above 808 MHz. In particular, intermodulation (IM) spurs are prone to being created in the LTE receive path causing desense in this path.
Accordingly, it would be desirable to have a means of negating such spurious emissions in a portable multiband radio. In particular, the ability to eliminate spurs in an active LTE receive path during the presence of simultaneous transmit LTE and transmit LMR transmissions is highly desirable.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.